1. Field of the Invention
The present invention generally relates to a color synchronizing circuit. More specifically, the present invention relates to a novel color synchronizing circuit for use in a color television receiver and a video reproducing apparatus such as a video disc apparatus or the like.
2. Description of the Prior Art
Since a color television signal is transmitted with a color signal carrier (a color subcarrier wave) suppressed, it is necessary to generate on the part of a receiver a color subcarrier wave of 3.579545 MHz being applied to a color demodulator (which generally comprises an R-Y demodulator and a B-Y demodulator) for the purpose of demodulation of a color signal by means of synchronous detection in a receiver. Accordingly, it is necessary to accurately control an oscillator for generating a color subcarrier wave with a color burst. It has been a common practice to employ a phase locked loop type color synchronizing circuit in which a color subcarrier wave generator is implemented by a voltage controlled oscillator, the phase of the output of the voltage controlled oscillator and the phase of the color burst extracted from the received signal are compared and the frequency and the phase of the voltage controlled oscillator are controlled responsive to the comparison output.
Such a color synchronizing circuit employing a phase locked loop is well known as an automatic phase control system, often simply referred to as an APC system. A conventional APC system has adopted a quartz vibrator as an oscillating unit for a voltage controlled oscillator. A quartz vibrator has a large quality factor and hence has an extremely small frequency deviation .DELTA.f up to a 3 dB attenuation point. For this reason a frequency variable range of the voltage controlled oscillator is as wide as .+-.700 Hz. On the other hand, the color burst of a color television signal is generally transmitted with a stabilized frequency. However, in the case of a video disc and other video reproducing apparatus, for example, a color burst is not always reproduced with stability but rather a frequency deviation is unavoidably involved. Even in the case of television broadcasting, an apparent frequency deviation takes place in the color burst in the case where a reception electric field intensity is weak or an external noise is large. A conventional APC system involved a problem that a frequency variable range of a voltage controlled oscillator is narrow, which makes it difficult to well follow a frequency deviation of a color burst as described above. As another approach in utilizing a conventional quartz vibrator, two quartz vibrators have been used to widen the frequency variable range. However, since quartz vibrators are expensive, employment of such expensive quartz vibrators makes expensive a color synchronizing circuit itself as a matter of course.